What is the difference between hard money and soft money? Or between Medicare and Medicaid? These are just a few of the many well-used - but often misunderstood - terms in US politics.

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Reagan Democrat Democratic voters who defected from their party to vote for Republican candidate Ronald Reagan in the 1980 and 1984 presidential elections, largely because of his social and fiscal policies.

The term is also used these days to denote moderate Democrats who are more conservative than other Democrats on issues such as national security or immigration.

By a vote of seven to two the court justices ruled that governments lacked the power to prohibit abortions. The court's judgement was based on the decision that a woman's right to terminate her pregnancy came under the freedom of personal choice in family matters as protected by the Fourteenth Amendment.

The decision remains one of the most controversial ever made by the Supreme Court.

Running Mate Once a party has selected its presidential nominee, the chosen candidate picks a political colleague, known as a "running mate", to run with him or her in the presidential election and who - if elected - will become vice-president.

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Second Amendment The so-called "right to bear arms" amendment to the US constitution, ratified in 1791.

The preamble reads: "A well-regulated militia being necessary to the protection of a free state, the right of the people to keep and bear arms shall not be infringed." But the wording is open to interpretation and as a result it has become the focus of fierce debate between supporters and opponents of gun control.

Gun control opponents such as the National Rifle Association argue that the amendment gives Americans the constitutional right to bear arms free from any form of government control. But advocates of gun control say the amendment was written in the days of the "Wild West" - which are now long gone - and only guarantee a right to bear arms as part of a collective militia.

Senate Generally considered to be the upper house of the United States Congress, although members of the other house - the House of Representatives - traditionally regard it as a co-equal body.

The Senate has 100 elected members, two from each state, serving six-year terms with one-third of the seats coming up for election every two years. The vice-president serves as the presiding officer over the Senate, although he does not serve on any committees and is restricted to voting only in the event of a tie.

Senate Majority Leader The leader of the majority party in the Senate, the Senate Majority Leader, is the most powerful member of the upper house of Congress.

He or she controls the daily legislative programme and decides on the time allowed for debates.

Senate Minority Leader The leader of the minority party in the Senate.

He or she acts as a figurehead for the minority party in the Senate, articulating its policy positions and attempting to deliver its legislative priorities.

Senator Member of the Senate, the upper house of Congress. Each US state has two (a junior and a senior senator, distinguished by length of service). In 2008 the presumptive nominees from both main parties are senators. The last time a senator was directly elected to the White House was in 1960, when John F. Kennedy won the presidency.

Soft money "Soft money" refers to political funds raised outside the regulations and laws of the Federal Election Campaign Act, and has been the main target for advocates of campaign finance reform.

Soft money had to be deposited in non-federal party accounts - at state level - and could not be used in connection with federal elections. A series of legal loopholes were used to get around this technicality, until the practice was banned by the McCain-Feingold law in 2002.

Many states allow individuals - as well as companies and unions (who are prohibited from giving directly to federal candidates) - to give unlimited amounts direct to state parties. Prior to McCain-Feingold this could be spent on grassroots organising, advertising and voter drives that indirectly helped all the party's candidates, including presidential candidates.

In the 2008 presidential campaign, the two parties raised nearly $1bn, from corporations, unions and individuals.

Speaker of the House The House Speaker is the leader of the majority party in the House of Representatives (not to be confused with the House Majority Leader).

He or she has a dual role as both the leader of his or her party in the House, and as the presiding officer in the chamber, with responsibility for controlling debate and setting the legislative agenda.

Under the terms of the Presidential Succession Act of 1947, the speaker is the second in line to the presidency after the Vice-President.

Stump speech On the campaign trail, candidates often deliver a generic speech, known as their "stump speech", outlining their core campaign messages.

The speech can be tailored to suit specific audiences, and may change as voter's concerns evolve over the course of the campaign.

The phrase stems from the days when candidates would make speeches standing on tree stumps. Campaigning politicians were said to be "on the stump".

Supermajority Some important votes require more than a simple majority - 50%-plus-one of those voting - to be carried. This is known as a supermajority.

For example, for an amendment to be added to the US constitution, it must be approved by a supermajority of two-thirds in both houses of Congress.

In the Senate, a supermajority of 60% is required to pass a motion of cloture ending a filibuster.

Super Tuesday First established during the 1988 campaign, Super Tuesday refers to a critical date in the campaign calendar - usually in early March - when a large number of states hold primary elections.

The hope was that by holding their votes on the same day they would increase the influence of the South and downplay the importance of the earlier New Hampshire primaries and Iowa caucuses.

Since then a number of other states have chosen to hold their primaries on the same day, including California.

However, other states, like Michigan and Florida, attempted to upstage Super Tuesday by holding primary elections of their own in January.

The idea that Super Tuesday would be the decisive event in the primary season was disproved in the 2008 election cycle, when Senator Hillary Clinton failed to break through despite victories in some big states on that date.

Suspending a campaign Candidates seeking the Democratic or Republican nomination can suspend their campaign, if they want to keep open the option of reviving it at a later date or play the role of power-broker at the party convention.

Candidates who have suspended their campaigns are able to direct their pledged delegates to support one of the other candidates for the nomination at the convention.

These delegate-votes may serve as a bargaining chip, if the candidate wants the promise of a job in the eventual nominee's possible future administration.

In 2008, John McCain also said he was suspending his campaign during a key stage in the financial crisis, only to resume it two days later.

Swift-boating If politicians on the left of the US political spectrum believe they are being unfairly attacked or smeared, they will often refer to the attacks as "swift-boating", in reference to the series of anti-John Kerry adverts aired in the run-up to the 2004 presidential election by a 527 group called the Swift Boat Veterans for Truth.

The adverts featured veterans who - like Mr Kerry - served on naval craft known as "Swift Boats" in Vietnam and who were critical of Mr Kerry's record in the war.

Swing states Swing states are, in the most simple terms, states in which the outcome of the vote is uncertain or close.

The most remarkable swing state is Missouri, which has backed every successful presidential candidate in the 20th Century except Dwight Eisenhower in 1956.

It carries only 11 votes in the electoral college, however, whereas larger states carry more weight, bringing candidates closer to the 270 votes needed to win.

In the most recent elections in 2000 and 2004, Florida and Ohio has been two of the most closely fought states. Each has a large number of electoral votes.

However, in the 2008 election some states which were considered solidly Republican, like Virginia and North Carolina, have become swing states, while others that were close in previous elections, like Iowa and New Mexico, appear to be solidly Democratic.

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Third-party candidate A candidate who does not belong to one of the two main US political parties, the Republicans or the Democrats.

No third-party candidate has ever won the Presidency, but they have may have strongly influenced the result in 1992, when Ross Perot took votes away from incumbent George HW Bush and helped Bill Clinton to victory.

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Vice-president The vice-president's primary duty is to succeed to the presidency in the event of the resignation, removal or death of the incumbent president.

The vice-president's only other constitutional responsibility is to preside over the US Senate and to use his vote as the decider in the event of a tie. This is only overridden when the Senate is conducting an impeachment trial against the president.

Early vice-presidents had little else in the way of official responsibilities. In 1885 Woodrow Wilson, who would later become president, commented that there was "little to be said about the vice-president... His importance consists in the fact that he may cease to be vice-president."

In recent years, though, vice-presidents have taken on an increasingly prominent role managing a range of high-profile foreign and domestic policy programmes.

Voting machine An apparatus for use by voters at polling stations that mechanically records and counts votes.

The machines come in many different forms and use various mechanisms to record votes, including punch cards, mechanical levers, optical scanning, and direct electronic recording.

Voting machines have come under intense scrutiny in recent years, with critics expressing concerns that electronic machines offer inadequate safeguards against fraud.

One leading company of voting machines, Diebold Election Systems, became a focus of controversy when it emerged that its chief executive, Walden O'Dell, had been a fundraiser for the Republican Party. He left the company (now known as Premier Election Solutions) in 2005.

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Wedge issue An issue that a politician might raise in order to drive a wedge between different groups within his opponent's supporter base.

An example of a wedge issue might be same-sex marriage: Republicans might propose to ban it in order to attract voters who support the Democrats on most economic issues, but who feel strongly about social issues.

Conversely, Democrats might highlight their more liberal position on abortion, in an attempt to win over pro-choice Republicans.

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527 Organisations Named after a section of the US Tax code, 527 organisations are political campaign groups officially unaffiliated to individual parties or candidates, and therefore not subject to campaign spending restrictions.

The groups have gained in prominence since 2002, when the McCain-Feingold campaign finance reforms were passed, cracking down on the use of "soft money" in election campaigns.

Examples of 527 groups include the Swift Boat Veterans for Truth, which ran a series of adverts during the 2004 presidential election attacking John Kerry's Vietnam War record, and MoveOn.Org's Voter Fund, which targets Republican candidates.

Critics of 527 groups say they are little more than front organisations allowing official campaigns to run expensive attack adverts without having to adhere to campaign finance restrictions.

They cannot directly urge the public to vote for or against particular candidate.

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